Device for testing the tightness of containers

ABSTRACT

An apparatus for testing the tightness of containers such as aerosol containers in which there are means for heating the containers, means for detecting leakage of gases from the containers and means for removing containers having leaks. The containers are heated by a high frequency electrical field and passed through a suction detecting means which actuates the container removal means upon detection of any leaked gases.

limit Almsore 1 Sept. 11, 1973 DEVICE FOR TESTING THE TIGHTNESS OFCONTAINERS [75] Inventor: Jun-gen Ahnsorge, Hamburg,

Germany [73] Assignee: Hans Schwarzkopf GmbH,

Hamburg, Germany [22] Filed: May 6, 1970 [21] Appl. No.: 35,205

[30] Foreign Application Priority Data May 6, 1969 Germany P I9 23 012.7

52 US. Cl. Q. 73/454 [51] llnt. Cl. 601m 3/16 [58] Fieldof Search73/40.7, 40, 49.2, 73/493, 37, 45.1, 41.4, 41; 2l9/10.69

[56] References Cited UNITED STATES PATENTS 3,251,976 5/1966 McBrien219/1069 FOREIGN PATENTS OR APPLICATIONS 1,063,006 3/1967 Great Britain73/493 Primary ExaminerS. Clement Swisher AttorneyBacon and Thomas [57]ABSTRACT An apparatus for testing the tightness of containers such asaerosol containers in which there are means for heating the containers,means for detecting leakage of gases from the containers and means forremoving containers having leaks. The containers are heated by a highfrequency electrical field and passed through a suction detecting meanswhich actuates the container removal means upon detection of any leakedgases.

1 Claim, 3 Drawing Figures Patented Sept 11, 1973 3 Sheets-Sheet 2 FIG.2

INVENTOR. JURGEN AHNSORGE BY L I Agent Patented Sept. 11, 1973 3Sheets-Sheet 5 1 a 3 4 2 0 w 1 3 r V O m U M 1m lllll l|.ll||| I I O m wr -I r W 8 no wd 1 2 1 m 3 FIG. 3

INVENTOR. JURGEN AHNSORGE Agent DEVICE FOR TESTING THE TIGHTNESS FCONTAINERS The invention relates to a device for testing the tightnessof containers, especially aerosol cans.

The law requires that aerosol cans be heated to 50C after being filled.At this temperature, the internal pressure in the can, which at a normaltemperature of C amounts to about three atmospheres, rises to aboutseven atmospheres. If the aerosol can withstands this pressure withoutdamage, it may be released for sale.

The cans are also normally tested for tightness, and cans having leaksare not used, since even at the normal temperature of 20C, any leak inthe can results 'in the slow escape of the propellant gas and after abrief period of the storage the can contains the active substance but nomore propellant gas. This makes it impossible for the consumer to removethe active substance from the can.

Aerosol cans have hitherto been heated in a water bath, the temperatureof which is somewhat above 60C. in this type of testing carried out in awater bath, cans having leaks are recognized by the bubbles ofpropellant gas issuing to a greater or lesser degree from the fullyimmersed can. This requires a crew of one or two men to observe the cansas they pass through the bath and to remove leaky cans by hand. Apartfrom the fact that this is not a sure means of detecting defective cans,the crew is in great danger of being injured, since it is quite possiblefor a can heated to 60C to explode.

The test baths have a capacity of up to 500 aerosol cans. This meansthat the water baths are up to twenty metres in length and thereforerequire a considerable amount of space. The water in the bath isheatedby means of electrical heater bars or steam coils, the watertemperature being kept constant by means of thermostats. The temperatureof water baths of this kind is dependent upon, among other things, thespeed at which the aerosol cans travel through the bath, since the saidcans pick up a certain amount of heat as they pass through the bath. ifthe throughput of cans is high, so much heat may be removed from thebath that the water temperature may quite easily drop below 60C. In thatcase the cans would leave the bath at a temperature below 50C, so thatthe test pressure required by law cannot be maintained at a highthroughput of cans. The water bath also has other deficiencies. Forexample, the pressure and/or tension of the water may not allow the gasto escape when the leak is small, and hubbles frequently emergeunnoticed if they are very small.

Another disadvantage of using water baths isthat the cans must pass to adrying unit after passing through the bath. This is necessary becausethe upper portion and head of the conventional aerosol can are usuallyconcave and water collects in these cavities and remains therein afterthe can leaves the water bath. Unless this water is removed and the canis dried, a danger of corrosion exists.

It is the special aim of the invention to eliminate the disadvantages ofthe known method of testing containers for tightness, and to produce adevice in which the internal pressure is higher than the externalpressure, whereby testing for tightness may be carried out very simply,very rapidly, and with no danger to the operating crew.

According to the invention, this aim is accomplished by heating the cansby means of a device operating at high frequency and by using a suctiondetector device for detecting leaky cans.

According to the present invention, after being filled with the solutionof active material and propellant gas, the aerosol cans pass through ahigh frequency field, where they are heated to the required testtemperature within about ten seconds. In view of the ease and rapiditywith which high-frequency energy can be controlled, it is easily adaptedto the throughput of cans, and fluctuations in the number of aerosolcans to be tested have no effect upon the amount of energy absorbed percan. In other words, cans of the same con tent leave the high-frequencyfield at the same temperature, i-.e. a temperature of substantially 50C.This makes it possible to maintain pressure tolerances much closer thanthose obtainable with existing methods of operation.

After leaving the high-frequency field, the cans pass on a conveyor tothe detector device where they are tested for leaks. The suctiondetector device will preferably have a housing containing a passage forthe cans, the width of the said passage approximates the width ordiameter of the can to be tested, and the said passage contains aplurality of detectors.

The detector device preferably has a suction tube or hose, the free endof which is connected to the can passage while the other end isconnected to the suction side of a constantly driven blower, thepressure side of which is connected to the detector electrode.

Additional characteristics essential to the invention may be gatheredfrom the following description.

The invention is described hereinafter, by way of example, withreference to the drawings. 7

FIG. 1 is a schematic side elevation in part section of a unit accordingto the invention;

, FIG. 2 is a sectional view along the line 2-2 in FIG.

l; and

FIG. 3 is a sectional view along the line 3-3 in FIG. 1.

The leak-testing unit according to the invention has an endless conveyor10 on which the cans pass consecutively through the heating device, thedetector device, and the sorting device.

The conveyor 10 has an endless belt 11 and a sliding track 11a,preferably of wood or plastic, so that there is little friction betweenconveyor belt 11 and track 11a. Guide strips 11b are provided laterallyof the said conveyor belt ill.

The heating device has a high-frequency coil 1 provided with power froma source not shown in the drawing. Coil I is provided with. a tube madeof electrically conductive material such as copper, the beginning andend of the said tube being tunnel-shaped, while the legs thereof runsubstantially horizontally between these ends on each side of the cantrack, as shown in FIG. I in dotted lines. Coil 1 is preferably hollowso that a coolant, for example water, may circulate through the coiltube. The electric power connections and the inlet and outlet for thecoolant are marked 2 and 3.

If the cans to be tested are made of sheet metal, it is of advantage forthe power to be in the frequency range between 400 500 KHZ and in themedium wave range. A shorter wave length may be used for plastic cans.

For the purpose of shielding the high-frequency coil from itsenvironment, a jacket 20, preferably of sheet copper, is provided whichsurrounds the coil substam tially completely. Jacket 20 surrounds coil 1on all sides. Arranged on one lateral wall of jacket 20, in spacedrelationship to each other, are one or more removable covers 4 providedwith observation windows, so that cans 5 travelling through the heatingunit may be observed from the outside.

Each cover 4 is provided with an electric safety lock whichautomatically cuts off the supply of power to high-frequency coil 1 whena cover is removed. The relevant safety contacts 6 are shown in FIG. 2.In order that the cans travelling through the high-frequency device maybe properly observed, lighting may be pro vided within shielding 20.Internal illumination of this kind is indicated schematically at 9.

High-frequency coil 1 is insulated from the frame of conveyor 10 andfrom shielding 20. This may be accomplished, for example, by means ofinsulating supports 8, of which two are illustrated in FIG. 2.

In order that the run of conveyor 11 passing through the coil chambermay be insulated, this run passes over an insulating element 11aextending over the length of the heating chamber and preferably made ofhardwood, hard rubber, or the like. In other words, the deviceinsulating the top run of conveyor 11 is made of a material having a lowcoefficient of friction. This prevents the build up of harmful stressesboth in shielding and in the metal parts of the conveyor frame.

As shown in FIG. 2, the bottom run of conveyor 11 runs in a channelformed below the heating chamber. Details of the conveying device arenot given, since they are not a part of the invention.

The heating device is supported as a whole in an appropriate fashion forinstance by means of supports such as those shown in FIG. 1.

The heating device is followed by a detector device 30, the latterhaving a chamber consisting of an upper box 31 and two lateral boxes 32,between which there is a passage for cans 5 (FIG. 3).

Arranged one behind the other in upper box 31 are one or more groups ofdetectors. Each group has two detectors with suction hoses or tubescommunicating at one point with the can track which is preferablylocated about twenty mm above conveyor 11. It was found that thislocation produces a satisfactory response from the detectors, mainlybecause the gases emerging from a leak (fluorinated-chlorinatedhydrocarbons) are heavier than air.

Located in the inlet region to detector chamber 31, 32 is a lightbarrier 17 consisting of a source of light and a photo-electric cell. Atthe outlet from detector chamber 31, 32 is another light barrier 12consisting of a source of light and a photo-electric cell. Theindividual groups of detectors are arranged between the two lightbarriers 17 and 12. In the embodiment described, only one group ofdetectors is provided, consisting of detectors l4 and 16. Each detectorhas a hose 14a, 16a made of plastic which, as shown in FIG. 3, runsdownwardly from the detector housing and communicates with the canpassage. The exact way in which the hose passes to the junction with thecan passage is not critical.

Each detector 143, 16 has a suction blower (not shown) which is switchedon at the start of the testing operation and thereafter operatescontinuously. Arranged on the suction side of the blower is a changeovervalve 15, 18 which connects the suction side of the blower selectivelyto suction hose 14a, 160 or to outside atmosphere. Arranged betweenfirst light barrier l7 and detector group 14, 16, according to thedrawing, is an air-supply device, the outlet aperture of which pointsgenerally forwards and downwards in relation to the direction of motionof cans 5. The said air-supply device has a blower 19 and acompressed-air valve 19a. The purpose of this will be describedhereinafter.

The detectors are in the form of suction detectors. This means that theatmosphere to be investigated is drawn into the detector, the componentsin the medium drawn-in, which are to be detected, being placed ordeposited upon an electrode or the like. The electrode responds to thedeposition of such materials, and delivers a signal indicating thepresence thereof. Thereafter, in order to be prepared for a new test,the electrode must be regenerated, i.e. the materials placed ordeposited thereon must be removed. In known detectors, this is usuallyaccomplished by burning the material off.

The detector device is succeeded by a selecting or ejecting device 40which may be of conventional design having, for example, anelectro-magnetically operated switch-point or a device operating withcompressed air which pushes the cans out as required.

Ejecting device 40 is succeeded by a safety switch 50 coupled toconveyor 11. This immediately cuts off the supply of power tohigh-frequency coil 1 if the said conveyor comes to a halt. Thiseffectively prevents any overheating of cans 5 in the heating chamber ifconveyor 11 is inadvertently stopped.

The throughput of cans may be increased by selecting an appropriatenumber of detectors.

Detector device 30 operates as follows:

When the device is started up, change-over valves 15, 18 are set in sucha manner that the suction blowers of detectors 14, 16 are connected tothe atmosphere. However, one of detectors 14, 16 is arranged to be in astate of readiness so that, after an additional signal s is applied, thedetector which is in the state of readiness can be switched to thetesting state, in which the suction hose is connected to the suctionside of the blower.

If a can passes light barrier 17, this produces a signal which switchesdetector 14 or 16, whichever is in the readinesss stae, into the testingstate, this being accomplished by changing over valve l5, 18. Assumingthat can 5 has no leak, the detector which is in the testing state doesnot respond. When can 5 passes through rear light barrier 12, anothersignal is produced, and this changes over detectors 14, 16 in such amanner that the detector hitherto in the testing state now passes to theinactive position, while the detector hitherto in the inactive positionnow passes into the readiness state. Assuming that incoming can 5 has aleak, the detector which is in the testing state responds and produces asignal. This signal is released when can 5 passes through second lightbarrier 12, and is applied to ejecting device 40. A delay is used toensure that the ejecting device becomes effective at the moment when thecan in question reaches it.

In the case of a leaky can, when the can passes light barrier 12, thedetectors are switched over as described above, and the signal producedwhen the said can passes through light barrier 12 is used to activateairsupply device 19, 19a for a short time, in order to restore theatmosphere in the can passage to its original state. The main purpose ofthis is to prevent the detectors from responding erroneously. Whetherblower 19 of compressed-air valve 19a is used depends upon thethroughput of cans. If the throughput is low, the relatively lowpressure of blower 19 is sufficientyfor' high throughputs, the higherpressure from valve 19a is used.

In its simplest form, ejecting device may have a compressed-air nozzle,actuated as described above and blowing the relevant can off theconveyor.

According to another preferred embodiment, ejecting device 40 mayexhibit a switch-point. When this is actuated, the guide strips onconveyor 1 l in the vicinity of ejecting device 40 are moved sideways,so that the rejected can is carried away by conveyor 11 on to anothertrack. A turntable,'for example, may be used to collect rejected cans.When the turntable is full, the cans are removed in order to bedestroyed.

What I claim as my invention is:

i. Apparatus for testing the tightness of containers as the containersmove through the apparatus, the apparatus comprising:

means adapted to pass the containers through the apparatus;

means fixedly positioned adjacent the passing means through which thecontainers pass; a pair of gas detectors adapted to detect the presenceof gas leaking from the containers; gas removing means adapted to directgases from the passage to the gas detector, the gas removing meansincluding a blower and a pair of tubes having respective first endsconnected to the passage and respective other ends connected to thesuction side of the blower and valve means coupled to the tubes forselectively connecting the tubes either to the blower or to atmosphere;the detector means further comprising: first light barrier means on theside of said detector near the entrance to said passage and capable ofactuating said valve means upon passage of a container past said firstlight barrier to connect the tube of one of said detectors to theblower, and a second light barrier means on the side of the detectornear the exit from said passage capable of actuating said valve meansupon passage of a container past said second light barrier to disconnectthe tube of said connected detector from the blower and connect the tubeof the other detector to said blower; and

means operable by said detecting means and adapted to remove leakingcontainers from the passing means.

t i i t i

1. Apparatus for testing the tightness of containers as the containersmove through the apparatus, the apparatus comprising: means adapted topass the containers through the apparatus; means fixedly positionedadjacent the passing means for heating the containers; detecting meansfixedly positioned adjacent the passing means to receive containers fromthe heating means and comprising: A housing having a passage throughwhich the containers pass; a pair of gas detectors adapted to detect thepresence of gas leaking from the containers; gas removing means adaptedto direct gases from the passage to the gas detector, the gas removingmeans including a blower and a pair of tubes having respective firstends connected to the passage and respective other ends connected to thesuction side of the blower and valve means coupled to the tubes forselectively connecting the tubes either to the blower or to atmosphere;the detector means further comprising: first light barrier means on theside of said detector near the entrance to said passage and capable ofactuating said valve means upon passage of a container past said firstlight barrier to connect the tube of one of said detectors to theblower, and a second light barrier means on the side of the detectornear the exit from said passage capable of actuating said valve meansupon passage of a container past said second light barrier to disconnectthe tube of said connected detector from the blower and connect the tubeof the other detector to said blower; and means operable by saiddetecting means and adapted to remove leaking containers from thepassing means.